1. Field of the Invention
Embodiments of the invention relate to a display device having touch sensors and a method for transmitting touch coordinate data thereof.
2. Discussion of the Related Art
A touch screen has replaced button switches as a user input device due to the trend of light weight and thin profile of household appliances and electronic devices. A touch screen includes a plurality of touch sensors. A capacitive touch screen includes Tx electrode lines, Rx electrode lines crossing the Tx electrode lines, and sensor nodes formed at crossings of the Tx electrode lines and the Rx electrode lines. Each of the sensor nodes has a mutual capacitance.
A display device includes a touch screen driver which senses changes in voltage changed to the sensor nodes before and after a touch operation and decides a contact position of a conductive material. The touch screen driver includes a touch controller and a touch screen driving circuit.
The touch screen driving circuit applies a driving pulse to the Tx electrode line connected to a Tx channel and receives voltages of the of the sensor nodes through the Rx electrode lines. Each time the touch screen driving circuit senses the voltage of each sensor node, the touch screen driving circuit samples the sensor node voltage received through the Rx electrode line and then converts the sampled sensor node voltage into digital data, i.e., touch raw data. The touch screen driving circuit then transmits the touch raw data to the touch controller.
The touch controller applies a setup signal to the touch screen driving circuit and sets the Tx channel and an Rx channel, which will sense the sensor node voltage. The touch controller analyzes the touch raw data using a touch recognition algorithm program embedded therein and outputs touch coordinate data. The touch coordinate data output from the touch controller is transmitted to a host system. The host system runs an application which a touch coordinate value indicates.
The touch controller may transmit the touch coordinate data to the host system using HID human interface device) transmission manner in Windows 7 or I2C transmission manner. With the recent development of multi-touch technology, the touch recognition number (i.e., the touch group number) increases to be equal to or greater than 10, and thus the touch coordinate number greatly increases. Because the HID transmission manner uses USB communication having a fast data transmission speed, it takes a relatively short time to transmit the touch coordinate data even if an amount of touch coordinate data increases. On the other hand, because a maximum transmission frequency is limited to about 400 Khz in the I2C transmission manner, the I2C transmission manner may generate the problem if an amount of touch coordinate data to be transmitted increases.
As shown in FIG. 1, one touch frame includes a first period P1 in which touch sensing is performed, a second period P2 in which a touch recognition algorithm is performed, and a third period P3 in which the touch coordinate data is transmitted. Thus, in the I2C transmission manner having a slow data transmission speed, the third period P3 becomes an important factor for determining a touch report rate.
The related art I2C transmission manner is used to transmit a full touch coordinate packet including touch coordinate data of all of touch groups. The full touch coordinate packet includes not only touch coordinate data of an effective touch group, on which the touch operation is performed, but also touch coordinate data of an ineffective touch group, on which the touch operation is not performed. For example, as shown in FIG. 2, when 11 touch groups T1 to T11 are set and the effective touch group, on which the touch operation is performed, is set to two touch groups T4 and T8, the related art I2C transmission manner further includes the ineffective touch groups T1 to T3, T5 to T7, T9 to T11, on which the touch operation is not performed. Hence, the touch coordinate data of all of the touch groups T1 to T11 is configured as the full touch coordinate packet and transmitted.
FIG. 3 illustrates a transmission format of the touch coordinate data included in the full touch coordinate packet shown in FIG. 2. In FIGS. 2 and 3, Xn is horizontal touch coordinate data, and Yn is vertical touch coordinate data, where n is a natural number. When 12 bits are assigned to each of the horizontal touch coordinate data and the vertical touch coordinate data for the display of the horizontal and vertical touch coordinate data in consideration of a maximum resolution 4096 (horizontal resolution)*4096 (vertical resolution) of the touch screen, 3 bytes are required to represent touch coordinate data of one touch group. Thus, as shown in FIG. 3, an amount of data of the full touch coordinate packet is 33 bytes.
In the I2C transmission manner having the transmission frequency of about 400 Khz, a time required to transmit 1-byte data is about 25 μs to 30 μs including latency as shown in FIG. 4. Thus, a transmission time of the full touch coordinate packet consisting of 33-byte data is about 825 μs to 990 μs and considerably increases.
As described above, the related art I2C transmission manner is used to transmit the full touch coordinate packet including not only effective touch coordinate data (i.e., touch coordinate data of the effective touch groups) but also ineffective touch coordinate data (i.e., touch coordinate data of the ineffective touch groups). Hence, time required to transmit the touch coordinate data in one touch frame increases, and it is difficult to improve the touch report rate using the related art I2C transmission manner. Further, transmission efficiency of the related art I2C transmission manner is reduced because of an increase in an amount of transmitted data, and a transmission error thereof increases.